This project involves examination of the toxicologic effects of single and repeated exposures to sulfuric acid mist, nitrogen dioxide, or ozone upon nonspecific defense mechanisms of the lung, using the rabbit as an animal model. The basic mechanisms examined are reflex bronchoconstriction, mucociliary clearance from the tracheobronchial tree, and alveolar macrophage-mediated clearance from the repiratory region. Clearance is studied in unsedated animals using radioactively tagged tracer aerosols. Specific functional aspects of macrophages will be examined in vitro following in vivo exposures. In addition, histological analyses of lung tissue will be performed. Results of the macrophage and tissue assays will be related to overall clearance effectiveness. This study will provide information on the role of three major ambient air pollutants in altering essential lung defenses; such changes may be early stages in the progression towards chronic obstructive lung disease.